Building the Future with Robotic Additive Manufacturing

They don't call it disruptive for nothing. Additive manufacturing (AM) is not only transforming the way we make things. It's changing how engineers and part designers think. They have to forget the limitations imposed by conventional manufacturing methods and open their eyes to the design possibilities.

Possibilities that are expected to catapult the additive manufacturing industry to $17 billion by 2020.

There are several types of additive manufacturing processes, including selective laser sintering (SLS), stereolithography (SLA), and fused deposition modeling (FDM). All are digital manufacturing methods where CAD data is used to fabricate a 3D object by adding layer upon layer of material, whether it's liquid, powder or sheet, or some other type of material. Even human tissue. AM is used to create myriad structures, from dental appliances, to advanced aircraft components, or an entire bridge. It can also be artistic. Robots help make it possible.

Additive manufacturing and robotics. One technology relies on steady, repetitive motion to build each infinitesimal layer, over and over again. The other technology is renowned for its repeatability and control. It's as if they were made for each other. It's a match made in disruptive technology, in the future of manufacturing.

Layer by Layer
At Midwest Engineered Systems Inc. (MWES) in Waukesha, Wisconsin, they are using laser additive manufacturing to create complicated metal parts that would otherwise be extremely difficult, if not impossible, to manufacture. A six-axis articulated robot drives the process, combining hot wire deposition and a laser to build metal parts layer by layer on an existing substrate. Exotic metals are deposited with precision and speed to build prototypes and small batches of high-value complex parts.

In this show floor demo, you see a propeller begin to take shape during the layer-by-layer process. Later footage in the same video shows a real-world application taking shape on the integrator's R&D system back in the lab in Wisconsin.

MWES named their patent-pending system ADDere, which was derived from the Latin word meaning to add. The process is similar to wire and laser additive manufacturing (WLAM), where a metal wire is fed into a melt pool generated by the laser beam on the substrate. The wire and substrate consequently form a metallurgical bond. The difference is that MWES is using a hot wire process.

"We heat the wire to the point that it's molten at the tip," explains Scott Woida, President and Founder of MWES. "Since the wire is already molten, we then use the right amount of laser power to melt the substrate underneath to form a strong bond. You're able to use less laser power when you're not trying to melt the wire as well as the substrate. The hot wire allows you to get higher deposition and put less heat into the part."

The process always starts with a substrate. In the case of the demo with the propeller, it's a cylinder. With other components, it may be a large steel plate or block.

"We can either use the substrate as part of the final part, or we can cut the substrate away and just have the part made of weld bead," says Woida. "But we have to start with something. It can be as simple as an eighth of an inch thick piece of steel."

Wire and Laser, plus Robot
The primary elements of the system include a high-precision industrial robot, the laser system, an integrated MIG wire and laser head, and the MWES controls system. The process includes active head control and dynamic deposition measuring to closely monitor the process before, during, and after the build.

To begin, CAD data is imported into CAD/CAM software, where it is prepared for the additive process. The part is then "sliced" into layers and the robot path is generated offline. Process information can be added automatically or manipulated manually. The generated path and process information is translated through a post processor and automatically transferred to the robot controller. Then the robot executes the program and builds the part layer by layer.

Applications include:

Prototypes

Small batch production runs

Replacement parts

Rebuilt surfaces

Cladding

The ADDere system uses a six-axis KUKA KR 90 HA (high accuracy) long-reach robot, which provides for path flexibility and a large working envelope. It's merged with a multi-axis part positioner. Woida says 2 m x 8 m x 40 m working ranges are possible.

Achievable tolerances are +/- 0.5 mm to +/- 1.5 mm, depending on deposition rate. Post-processing usually requires some machining. The additive process creates a hardened form of the material, so soft metal also requires annealing.

Freeform Fabrication, Less Waste
System advantages include rapid development of new metal parts, quick design changes without adding tooling costs, and low initial cost to production. Woida says one of the main advantages is the ability to take multiple part subassemblies and create them as one unit.

With MWES' ADDere system, solid freeform fabrication allows the use of different metals on different areas of the part to create engineered characteristics specific to an application. This is particularly cost-effective when you want to clad a less expensive metal with a more exotic metal for particular properties like high wear resistance. The process can also be used for repairs by first machining a part to a stable structure and then building up the part to its original state.

"We're getting properties similar to casting, closer to forged," says Woida. "Compared to subtractive methods, you waste less base material because you're building to near net shape."

"When we're running the wire for manufacturing our component, all that wire ends up getting used to make that part," he explains. "There is very little waste of the wire (as opposed to powdered metal AM processes where the excess powder falls by the wayside and needs to be recycled). The only thing that happens is that you're machining the outside of that component to get from your near net shape to your net shape. Typically you only machine your mating surfaces. You don't have to machine the whole part."

For the propeller in the demo cell, Woida says you may only need to machine about 5 percent of that part after the AM process.

He says it's also 10 times the speed of powder-based AM processes. "We can put down 32 pounds per hour of stainless steel right now, and that's with a 14 kilowatt laser. Soon we'll have a 20 kilowatt laser.

"When the material has a high dollar value and it's really hard to machine, this process makes sense," he adds.

Not suited for this process are small components, parts that have low manufacturing costs, and parts that require little machining from billet.

"When the part is done, it has a casting-like quality to it," says Woida. "You can either machine the part or we can use a laser to smooth out the outside for a better surface finish. But a lot of our customers are less interested in surface finish as much as they are functionality."

High-Value Parts, Exotic Metals
The ADDere system is available as a turnkey product for purchase or as a manufacturing service.

"The parts we are working on to date are basically validation for customers that we can make the components to their specifications," says Woida. "Mass production hasn't started, but we are providing sample sets to customers to verify the capability of the system. They are evaluating them for quality and then they will be buying them in larger quantities from us, or buying the system."

One of those parts undergoing testing in MWES' R&D system is seen in the second half of the aforementioned video. This is an 1,800-pound bulkhead for an aircraft carrier. Rather than having to waste valuable space with spare parts inventory on board the ship, imagine being able to use additive manufacturing to create or repair parts, on demand, while at sea.

The ADDere additive manufacturing system has application for aerospace, drive train, suspension, naval, military, oil and gas, construction, mining, and agricultural equipment. Materials best suited for these applications are typically exotic metals, such as stainless steel, aluminum, titanium, cobalt, Inconel, and tungsten alloys.

Woida says their experience in laser welding is paying off.

"We typically get involved in highly engineered systems, so we have a lot of exposure to the latest technologies, whether it's the latest laser technology or robotic technology. (MWES is an RIA Certified Robot Integrator.) On a daily basis, we design systems that don't exist in a catalog, that are highly engineered. You need a lot of diverse experience. You need mechanical engineers because these systems are fairly complex. You need software people to make this easy and viable to sell on the open market. You need robotic engineers to then integrate all that. You need weld engineers that can verify and make sure the metallurgical properties are what they're supposed to be. You need a whole lot of people to bring this together."

Hybrid laser weld processes like the MWES additive manufacturing system were just making their way into the conversation a few years ago when we discussed the latest laser welding technologies with Lincoln Electric's hybrid laser expert in Robots and Laser Welding, the Perfect Fit. He was excited about the potential for hot wire in laser additive manufacturing. Now it's on the job in America's heartland.

Metal Casting
Additive manufacturing and robotic automation are also ushering in a whole new digital world for the metal casting industry. Once again, the technologies are opening design engineers' eyes to a future with new possibilities. First, we have to go back to additive's origins at the Massachusetts Institute of Technology, where 3D printing was born. Where in the 1990s, MIT student Jim Bredt was working on his doctoral thesis investigating the creation of inkjet on powder technology.

The term 3D printing was originally used to describe how intermittent layers of powdered materials and liquid binder are dispensed in a programmed pattern to form a three-dimensional object. Bredt says the term was coined by his thesis advisor, and eventually adopted by industry at large. Now, 3D printing is often used interchangeably with additive manufacturing and it encompasses many different types of processes.

Bredt, who is Research and Development Director at Viridis3D in Woburn, Massachusetts, has nearly 30 years in the 3D printing industry, but he never lost sight of his first love. One of his specialties is ceramics and particularly mold making for metal casting. He had always been interested in metal casting, even as a kid. That may have helped him get into MIT. The university was intrigued with Bredt after discovering that in high school he built a foundry in his backyard.

Upon graduating from MIT, Bredt helped start Z Corporation in 1995. Z Corp. is credited for the first commercial introduction of inkjet-based 3D printing technology. Z Corp. was then acquired by 3D Systems, which is known for its cofounders who invented stereolithography.

Bredt eventually left 3D Systems to launch Viridis3D in 2010, where he was anxious to get back to metal casting. The goal was to build a 3D printing machine that was more versatile in the types of materials it could process and more hardened industrially to handle the rigors of working in a foundry. The new team at Viridis3D focused its sights on the sand casting industry.

"A lot of the components that you really need a 3D printer for are things you can't make by conventional processes, like cores especially, which can be very intricate," says Bredt. "It increases the capabilities of your process in such a way that you can take more risks in your design. You don't have to spend all that on tooling. If you 3D print a part and it's a failure because the design is too fragile, then you didn't really lose that much. By being able to take more risks in your design, it expands the gamut of geometric shapes that you can create with the technology."

Breaking the Mold
Among reimagining ways of making things, Bredt questioned how 3D printing machines were designed.

"A 3D printer is basically a robot with a material dispenser attached to it," explains Bredt. "When we created Viridis3D, I asked why should I try to build my own robot. My background is in materials, not in machine design. Why don't I just buy a robot? Then I can focus on material dispensing."

For Viridis3D, using an off-the-shelf industrial robot in its 3D printing system was a major break from the competition.

"Our use of a commercial robot is an interesting distinction," says Bredt. "Our competitors by and large use gantry systems to lug their much heavier printing engine around. By using an arm instead of a gantry system, our print head is designed to be light, rugged and reliable."

He notes that no motion control system comes without its complications.

"They each pose their own challenges. Having worked with gantry systems through my entire career before Viridis3D, I'm actually very happy with robot arms. Our cost is low because the robot is very economical. The accuracy and the load limit is very generous relative to what we need for our system."

3D Printing with Robots
While development was underway on its robotic additive manufacturing system, Viridis3D partnered with EnvisionTEC, a global provider of professional-grade 3D printing solutions. Now a wholly owned subsidiary, Viridis3D can continue to fund further development. Earlier this year, Viridis3D commercialized the first robotic 3D printer, the RAM 123.

The patent-pending system uses a standard four-axis ABB IRB460 robot to create sand molds and cores for casting metal parts. The robot is equipped with a powdered material feeder that distributes the sand and a print head that dispenses the liquid binder into the sand. Spreading sand and dispensing binder intermittently, the robotic 3D printer builds the mold layer by layer.

The print head can be heavy, especially when loaded with sand. So that's why Bredt says a four-axis robot, as opposed to a six-axis, is preferred because it has a larger load capacity.

"These printing elements really only work if they are held horizontally," he explains. "The print head travels in a plane and very gradually rises up. Four-axis is ideal because they are constrained to always travel in a plane, at least the wrist. It has a high load capacity and stays accurate."

Viridis3D's RAM system has an open architecture. The molds are built on a stationary table. The tabletop is a pallet that can be used to move parts on and off the machine with a forklift.

"Competitors' machines use a box of a fixed size to build the parts in," says Bredt. "Ours is an open table, so you can build parts of different sizes without having to fill the entire box with materials.

"One of the reasons we went to a stationary table is that it was clear to me during the later years at Z Corp., when we were building larger and larger machines, that pretty soon the substrate would weigh more than the machine," continues Bredt. "Some of the heavy foundry sand we use, if you fill up the box, weighs more than the machine."

How It Works
The process begins with the designer creating a CAD model. It gets uploaded. You open it with the desktop software, which simply waits for the print head to request data for each layer of the mold in sequence. Then it queues up a few layers in advance and sends data to the robot on a layer-by-layer basis.

"Our desktop software is similar to your print manager program that sends each page to a printer," says Bredt. "Except this is in 3D and there's a lot of algebra involved."

Viridis3D's proprietary desktop software is responsible for taking the data created on the CAD system and converting it into machine code used by the robot and the print head to actually build the mold. After the mold is built, you may need to wait a little while for the chemical reaction to cause it to solidify. It's then removed from the other sand piled on the table, brushed off, and taken to the foundry.

"You can pour molten metal right on top of it and it works just like a conventional mold," says Bredt. "The mold itself cannot be re-used. The sand material can be heat treated to clean it up (to separate it from the binder) and then used again. The sand left on the table that doesn't get made into the mold can just be scooped up and fed back into the machine."

Short Lead Times, Space Savings
For users of the RAM system, the main advantage is they can quote parts with a short lead time. Molds and cores with complicated shapes can be made without a lot of tooling. Going digital is also easier. Viridis3D customer Trident Alloys sees the future in this robotic additive manufacturing system. Watch the video

"Sand casting is still dominated by the old wooden pattern technology, where you take a box and you squish sand up against a wooden pattern to make a cavity of a certain shape," explains Bredt. "Then you assemble it into a mold to make a casting. It's a relatively quick process for making a mold. In fact, it's quicker than a 3D printer, but you have to have a warehouse somewhere where you keep the patterns."

Patterns become damaged or misplaced. The cost of warehouse space to inventory all those patterns continues to rise.

"Pattern-making is a dying art," says Bredt. "Companies with these 50-year-old patterns send in a guy with a can of Bondo to try and fix it. In some cases, all they have is drawings or maybe they have to reverse engineer existing product. People that buy our system really like the option of switching over to digital manufacturing, because you get rid of the overhead for storing those patterns. This is a perfect example of disruptive technology taking over old technology."

Bredt says they are widening their sights on other materials beyond sand that offer higher resolution, including plastic powders, ceramics, and even powdered metals. Robots will continue to shoulder the load.

From complex geometries and multi-material parts, to multiple subassemblies merged into one. Together, additive manufacturing and robotics will transform the way we think about manufacturing.